A tower crane jib luffing hydraulic system and control method

Abstract

The application discloses a tower crane movable arm luffing hydraulic system and a control method, and relates to the technical field of tower crane movable arm luffing hydraulic systems. The luffing hydraulic system comprises an oil tank, a motor, a plunger variable pump, a high-pressure filter, a first one-way valve, a pressure gauge, a pilot overflow valve, a proportional directional valve, a shuttle valve, a second one-way valve, a third one-way valve, an oil return filter, a luffing cylinder valve group, a luffing cylinder and a displacement sensor. The luffing cylinder valve group comprises a first balance valve, a first stop valve, a second stop valve, a second balance valve, a first pressure sensor, a third stop valve, a fourth one-way valve, a fifth one-way valve, a fourth stop valve and a second pressure sensor. The application can satisfy the stability and reliability of the luffing cylinder when the force direction and the force size of the luffing cylinder change in real time at different luffing angles, realizes adaptive matching of load, power and flow, satisfies maximum power utilization, reduces the heat generation of the system, reduces the energy consumption of the equipment, and has high control precision, fast response and long service life.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cranes, in particular to a tower crane arm luffing hydraulic system and control method. BACKGROUND

[0002] The tower crane is an important construction equipment, and is more and more widely used in urbanization construction. The traditional arm luffing mechanism of the arm luffing tower crane is generally composed of a motor, a brake, a speed reducer, a winding drum, a steel wire rope and an arm frame. The arm luffing is driven by the motor, and the arm frame is pulled by the steel wire rope to perform the tilting operation. However, the traditional structure of the arm frame is long and has a large running radius, which is not suitable for the operation in the urban high-rise building group, the narrow construction site and the crowded space. It is also very difficult to assemble and disassemble the tower crane on site.

[0003] Therefore, in the above working environment, the tower crane arm usually adopts a hydraulic luffing system, which is composed of a luffing cylinder, a hydraulic pump station and a control system. Compared with the traditional motor-driven steel wire rope pulling arm frame for luffing, the hydraulic luffing balance arm is shorter, the running radius is smaller, and it has more advantages in the urban high-rise building group, the narrow construction site. At the same time, it is very convenient to assemble, disassemble and transfer the tower crane on site.

[0004] It is known that the patent publication No. CN110422778A discloses a luffing hydraulic system of a lifting arm and a crane. The luffing hydraulic system comprises: a hydraulic cylinder for driving the tilting swing of the lifting arm, the hydraulic cylinder comprising a first cavity for discharging hydraulic fluid when the lifting arm is falling and a second cavity for introducing hydraulic fluid; a control valve comprising an inlet for introducing hydraulic fluid, a backflow port for discharging hydraulic fluid, a first fluid port and a second fluid port, the control valve having a first state in which the inlet is communicated with the first fluid port and a second state in which the inlet is communicated with the second fluid port; a balance valve connected between the first fluid port of the control valve and the first cavity of the hydraulic cylinder and having a control fluid port for introducing hydraulic fluid to control the opening of the balance valve, the control fluid port being communicated with the second fluid port of the control valve; and wherein the control valve further comprises a valve body having a first valve cavity, a first valve core movably arranged in the first valve cavity to switch the control valve between the first state and the second state, and a pressure reducing valve. When the lifting arm is rising, the control valve is reversed by mechanical operation, and the pressure oil output by the hydraulic pump enters the rodless cavity through the inlet P, the first fluid port and the balance valve, pushes the lifting arm to rise, and the hydraulic oil in the rod cavity is discharged back to the oil tank through the back pressure valve. When the lifting arm is falling under the action of gravity, the control valve is reversed by mechanical operation, and the pressure oil output by the hydraulic pump flows to the control port of the balance valve through the inlet P, the control valve, the pressure reducing valve and the B port. The pressure of the control pressure reducing valve is controlled to control the opening of the balance valve, so as to control the stable falling of the lifting arm.

[0005] However, the jib hydraulic system technology has the following problems when used in the tower crane jib: 1. The jib of the tower crane is subjected to the gravity of the counterweight, the jib frame and the load, and the force direction and the force size of the luffing cylinder change at different angles. When the luffing is lowered to the force of the counterweight being greater than the force of the jib frame and the load acting on the cylinder, the luffing cylinder is switched from compression to tension, and the hydraulic system must actively provide a retraction power to overcome the tension condition of the cylinder to prevent free fall. Therefore, the jib hydraulic system is not suitable for the tower crane jib hydraulic system. 2. The mechanical control lever directly drives the control valve, and the long-term wear and aging of the valve core and the sealing ring caused by manual operation and the gap in the mechanical transmission result in low control accuracy of the luffing action, affecting the work efficiency and safety. 3. The hydraulic pump in the jib hydraulic system has no load sensing function, and the hydraulic pump is always working at full load during the jib lowering process. The luffing hydraulic system generates a large amount of heat and is prone to overheating. 4. The jib hydraulic system does not have an effective protection mechanism such as overspeed, overpressure and overstroke, and is prone to cylinder out-of-control or hydraulic element damage in sudden conditions, which poses a safety hazard. SUMMARY

[0006] In view of the deficiencies in the prior art, the present application provides a tower crane jib luffing hydraulic system and a control method.

[0007] In order to achieve the above-mentioned purposes:

[0008] The present application provides a tower crane jib luffing hydraulic system, which comprises an oil tank, a motor, a plunger variable pump, a high-pressure filter, a first check valve, a pressure gauge, a pilot relief valve, a proportional directional valve, a shuttle valve, a second check valve, a third check valve, an oil return filter, a luffing cylinder valve group, a luffing cylinder and a displacement sensor.

[0009] The luffing cylinder valve group comprises a first balance valve, a first stop valve, a second stop valve, a second balance valve, a first pressure sensor, a third stop valve, a fourth check valve, a fifth check valve, a fourth stop valve and a second pressure sensor.

[0010] The hydraulic oil is stored in the oil tank, the motor is connected with the plunger variable pump, the oil suction port and the oil discharge port of the plunger variable pump are connected with the oil tank through the oil suction pipeline and the oil discharge pipeline respectively, the pressure oil port of the plunger variable pump is connected with the inlet of the high-pressure filter, the outlet of the high-pressure filter is connected with the inlet of the first check valve, the outlet of the first check valve is divided into three paths, the first and second paths are connected with the pressure gauge and the pressure port of the pilot relief valve respectively, and the third path is connected with the P" port of the proportional directional valve; the 1 port of the shuttle valve is connected with the B" port of the proportional directional valve, and the current is connected with the B1 port; the 2 port of the shuttle valve is connected with the A" port of the proportional directional valve, and the current is connected with the A1 port; and the middle 3 port of the shuttle valve is connected with the pilot pressure oil port X of the plunger variable pump.

[0011] The oil discharge port of the pilot overflow valve, the T" port of the proportional directional valve, the inlet of the second check valve, and the outlet of the third check valve are converged and connected to the T3 port. The outlet of the second check valve is connected to the oil tank through an oil return filter, and the inlet of the third check valve is connected to the oil tank as an oil suction port.

[0012] The A2 port is connected to the 2 port of the first balance valve and the 3 port of the second balance valve, and the 3 port of the second balance valve is a pilot port. The B2 port is connected to the 2 port of the second balance valve and the 3 port of the first balance valve, and the 3 port of the first balance valve is a pilot port. The 1 port of the first balance valve is divided into three paths and connected to the first stop valve, the check port of the fourth check valve, and the third stop valve. The 1 port of the second balance valve is also divided into three paths and connected to the second stop valve, the check port of the fifth check valve, and the fourth stop valve. The other end of the third stop valve is connected to the rodless chamber of the variable amplitude cylinder and the first pressure sensor, and the other end of the fourth stop valve is connected to the rod chamber of the variable amplitude cylinder and the second pressure sensor. The other ends of the first stop valve and the second stop valve are connected in parallel and then connected to the inlet of the fourth check valve and the fifth check valve, and then connected to the T2 port.

[0013] Further, the other end of the fourth stop valve is connected to the rod chamber of the variable amplitude cylinder, the second pressure sensor, and the pressure port of the safety valve.

[0014] The other ends of the first stop valve and the second stop valve are connected in parallel and then connected to the inlet of the fourth check valve, the inlet of the fifth check valve, and the unloading port of the safety valve, and then connected to the T2 port.

[0015] Further, the plunger variable pump is a Rexroth A11VO-LRDS series axial plunger pump with a displacement of 40-260 ml / r and a maximum pressure of 350 bar, integrating power control, pressure cutoff, and load sensing functions.

[0016] Further, the proportional directional valve is a three-position four-way Y-type pilot proportional valve with an input of 4-20 mA current signal. When the current signal increases from 12 mA to 20 mA, the control cylinder extends. When the current signal decreases from 12 mA to 4 mA, the control cylinder retracts.

[0017] Further, it also includes a PLC controller. The input end of the PLC controller is connected to the first pressure sensor, the second pressure sensor, the displacement sensor, and the variable amplitude up / down multi-gear switch signal set in the driver's room linkage platform.

[0018] The output end of the PLC controller is connected to the motor, the plunger variable pump, and the proportional directional valve. The PLC controller adjusts the displacement of the valve core of the proportional directional valve through the current signal to realize directional and flow proportional control.

[0019] The first pressure sensor is used for monitoring the pressure of the rodless chamber; the second pressure sensor is used for monitoring the pressure of the rod chamber; and the displacement sensor is used for monitoring the real-time stroke position of the boom cylinder.

[0020] Further, the PLC controller is also used for calculating the boom angle according to the stroke signal received by the displacement sensor and displaying the boom angle on the operation interface of the cab, and the calculation formula of the boom angle is as follows:

[0021] ,

[0022] Wherein, S is the length of the cylinder when the boom is horizontal; L1 is the length of the support frame;

[0023] L2 is the length of the boom fulcrum;

[0024] is the working stroke of the cylinder when the boom is being luffing;

[0025] α is the angle between the rod chamber fulcrum and the support frame when the boom is horizontal;

[0026] α' is the angle between the rod chamber fulcrum and the support frame when the boom is being luffing;

[0027] β is the angle between the rod chamber fulcrum and the horizontal plane when the boom is horizontal;

[0028] is the boom angle, which is the angle between the boom and the horizontal plane when the boom is being luffing.

[0029] Further, the PLC controller is also used for realizing the over-grade shift control of the luffing hydraulic system: when over-grade upshift is performed, the PLC controller realizes the smooth transition of the current signal through the incremental ramp algorithm, so that the hydraulic oil flow output by the piston variable pump is smoothly increased; when over-grade downshift is performed, the descending ramp algorithm is adopted, so that the hydraulic oil flow output by the piston variable pump is smoothly decreased.

[0030] Further, the PLC controller is also used for realizing the pressure protection control: when the load pressure reaches the preset cut-off value of the piston variable pump, the safety valve of the piston variable pump is opened to limit the system pressure; at the same time, the first pressure sensor monitors the pressure of the rodless chamber in real time and transmits the signal to the PLC controller, and if the pressure of the rodless chamber is abnormal or exceeds the threshold value, the PLC controller immediately triggers an alarm and executes the luffing action stop instruction, forming a double safety guarantee mechanism of pressure cut-off and real-time monitoring, to ensure the safety and reliability of the system under overload working conditions.

[0031] Further, the PLC controller is also used for realizing the intelligent stroke protection control: when the stroke position approaches the preset protection threshold value during the luffing up or down process, the PLC controller immediately triggers a deceleration instruction to make the system stop running smoothly.

[0032] Further, the PLC controller is also used to realize intelligent speed protection: in the case of unchanged gear, the PLC controller compares the gear normal speed with the real-time variable amplitude speed: when the variable amplitude speed rises to 110% of the gear normal speed, the gear current increment received by the proportional directional valve is reduced by 50%, the speed is automatically reduced, and the gear-up function is locked, only gear-down speed reduction can be realized; when the variable amplitude speed recovers to the gear normal speed, the rated current is reset and the gear-up limitation is removed;

[0033] If the variable amplitude speed continues to rise to 120% of the gear normal speed after the gear current increment is reduced by 50%, the PLC controller immediately stops the variable amplitude action and triggers an overspeed alarm.

[0034] The application also provides a control method applied to the tower crane boom variable amplitude hydraulic system.

[0035] Boom up: the operator presses the "oil pump on" button, the PLC controller controls the motor to be powered on, drives the plunger variable pump to operate, the operator pulls down the boom up 1 gear on the linkage table, the PLC controller receives the on-off signal of the boom up 1 gear, outputs the current signal corresponding to the gear to control the opening of the proportional directional valve, the plunger variable pump outputs the hydraulic oil flow corresponding to the opening, and the hydraulic oil flow is transmitted to the rodless cavity of the boom cylinder through the P" port, the A" port of the proportional directional valve, the first balance valve and the third shut-off valve, meanwhile, the second balance valve is opened under the action of the pilot pressure, the hydraulic oil in the rod cavity of the boom cylinder is transmitted from the fourth shut-off valve, the second balance valve, the B" port and the T" port of the proportional directional valve to the second check valve and the oil return filter to flow back to the oil tank, the boom cylinder is pushed out, and the boom starts to rise.

[0036] In the boom variable amplitude up process, the X port of the plunger variable pump receives the working oil pressure of the rodless cavity in real time through the shuttle valve, and based on the load sensing function, the pump body monitors the pressure difference between the input pressure and the output pressure of the proportional directional valve in real time; when the pressure difference increases, the pump automatically reduces the displacement; when the pressure difference decreases, the displacement increases, and the pressure difference is always maintained at a set value through dynamic adjustment.

[0037] During the boom variable amplitude up, the force direction and the force size of the boom cylinder are always changing, when the boom cylinder load is within the constant power control starting pressure range set by the plunger variable pump, the plunger variable pump can output the rated full flow at most, at this time, the boom running speed is directly controlled by the boom up gear of the linkage table; when the load exceeds the constant power starting pressure, the maximum output flow of the plunger variable pump will be automatically adjusted according to the power control characteristic curve, at this time, the constant power adjustment is prior to the gear adjustment, the maximum speed of the boom is dynamically limited to adapt to the load increment, thereby ensuring the stability and reliability of the system operation.

[0038] During the boom luffing up, the gear can be switched step by step according to the load and operation condition, such as acceleration;

[0039] During the boom luffing up, when the load pressure reaches the preset pressure cut-off value of the piston variable pump, the safety valve of the piston variable pump is immediately opened to limit the pressure from rising, thereby ensuring the safety and reliability of the system under overload conditions; at the same time, the first pressure sensor monitors the real-time pressure state of the rodless cavity in real time and transmits the pressure signal to the PLC controller; when the pressure of the rodless cavity is abnormal or exceeds the preset safety threshold, the PLC controller will quickly trigger an alarm signal and execute a luffing action stop instruction according to the pre-set overpressure protection parameters, forming a double protection mechanism.

[0040] When the boom luffing up reaches the working position, the operator will pull the gear to zero, and the PLC controller will output a current signal according to the descending slope algorithm to control the proportional directional valve to smoothly switch to the middle position, so that the boom luffing stops; at this time, the luffing cylinder is locked and pressure is maintained under the action of the first and second balance valves, and a motor delay power-off protection mechanism is triggered to ensure the safety and stability of the system.

[0041] The control logic for the boom descending is symmetrical to that for the boom ascending.

[0042] Further, the control method further includes the following when the gear is shifted by a step:

[0043] When the gear is shifted up by a step, the PLC controller realizes the smooth transition of the current signal through the incremental slope algorithm, so that the hydraulic oil flow output by the piston variable pump smoothly increases; when the gear is shifted down by a step, the descending slope algorithm is used to make the hydraulic oil flow output by the piston variable pump smoothly decrease.

[0044] Further, the control method further includes

[0045] The following is the response when the luffing approaches the limit stroke:

[0046] When the stroke position approaches the preset protection threshold during the boom luffing up or down, the PLC controller immediately triggers a deceleration instruction to make the system stop running smoothly.

[0047] Further, the control method further includes the following when the luffing cylinder is in a vacuum fault:

[0048] When the variable amplitude oil cylinder is subjected to the same direction load during the boom variable amplitude rising, the rodless cavity quickly sucks the oil tank hydraulic oil into the rodless cavity through the suction effect of the suction port, the third one-way valve, the T3 port and the T2 port, the fourth one-way valve, realizes oil supplement to prevent the boom from being unstable; at the same time, under the condition that the gear position is unchanged, the PLC controller compares the gear normal speed with the real-time variable amplitude speed in real time: when the variable amplitude speed rises to 110% of the gear normal speed, the gear current increment received by the gear position proportional directional valve is reduced by 50%, the speed is automatically reduced, and the gear increasing function is locked, only the gear decreasing speed can be decreased; when the variable amplitude speed returns to the gear normal speed, the rated current is reset and the gear increasing restriction is removed;

[0049] If the variable amplitude speed continues to rise to 120% of the gear normal speed after the gear current increment is reduced by 50%, the PLC controller stops the variable amplitude action immediately and triggers the overspeed alarm;

[0050] When the suction fault occurs during the boom variable amplitude descending, the rod cavity quickly supplements oil through the fifth one-way valve, the PLC control logic is symmetrical to the rising process, the current adjustment and speed protection mechanism in the opposite direction are executed, and a bidirectional symmetrical fault protection system is formed.

[0051] Compared with the prior art, the beneficial effects of the present application are:

[0052] 1、The boom hydraulic system of the present application is provided with a proportional directional valve, which realizes the extension and retraction of the variable amplitude oil cylinder by receiving the input signal of the PLC controller of the control box, and can adjust the size of the input signal value in real time according to the boom load condition, control the opening of the proportional directional valve, control the flow output of the plunger variable pump, and then control the speed of the extension and retraction of the variable amplitude oil cylinder, so as to realize the stable rising and descending of the tower crane boom, the control precision is high and the response is fast; the rodless cavity and the rod cavity are both provided with pressure type balance valves, the internal leakage is very low, the pressure maintaining demand of the boom long time locking operation can be met, and when the boom frame is at different running angles and the load direction changes, the stability of the variable amplitude oil cylinder during the extension and retraction under the same direction load can be ensured through the back pressure of the two balance valves, and the free fall phenomenon can be effectively prevented.

[0053] 2, The plunger variable pump of the application is power control type, with pressure cut-off and load sensing control function, when the boom is being luffing, the plunger variable pump sets the constant power control starting pressure through the constant power control function, when the load of the luffing cylinder is within the set constant power control starting pressure range, the plunger variable pump can output the rated full flow, when the load exceeds the constant power starting pressure, the maximum flow output by the plunger variable pump will be reduced and automatically adjusted through the constant power curve; at the same time, the pilot pressure oil port X of the plunger variable pump receives the real-time working oil pressure of the luffing cylinder through the shuttle valve, when the operator switches the gear to adjust the opening degree of the proportional directional valve to control the luffing speed, the system automatically compares the pressure difference between the input pressure and the output pressure of the proportional directional valve according to the load sensing function, when the pressure difference increases, the plunger variable pump automatically reduces the output displacement, when the pressure difference decreases, the plunger variable pump automatically increases the output displacement, until the pressure difference returns to the set value; the power control and load sensing function of the plunger variable pump realizes the adaptive matching of the load power, which greatly reduces the energy consumption while meeting the luffing speed requirement; when the load pressure of the luffing cylinder reaches the set pressure cut-off value, the safety valve of the plunger variable pump opens, and the pressure will no longer rise, which ensures the safety and reliability of the system under overload.

[0054] 3, The application significantly improves the operation performance of the boom luffing system through the cooperative control of PLC and the load sensing system, the system uses displacement sensors to monitor the real-time stroke position of the luffing cylinder, PLC calculates and displays the luffing angle in real time, which eliminates the conversion link of traditional angle sensors, has higher measurement accuracy, controls the opening degree of the proportional directional valve through the segmented slope algorithm to realize smooth transition of hydraulic oil flow during step shifting and effectively suppress system impact; the load sensing system dynamically adjusts the displacement of the plunger variable pump, maintains full flow output within the constant power range, and automatically limits the speed when overloaded; the slope algorithm is used to realize smooth braking during the shutdown stage, the balance valve locks the cylinder and delays power-off, which ensures the safety of the system; the scheme integrates displacement sensors for dual purposes and uses intelligent control strategy, which simplifies the system structure while ensuring accuracy, improves operation stability and safety.

[0055] 4, The application is most effective when used in the boom luffing hydraulic system of a tower crane, which can meet the stability and reliability of the luffing cylinder when the force direction and size change in real time at different luffing angles, realizes adaptive matching of load, power and flow, maximizes power utilization, reduces system heat generation and energy consumption, and has high control accuracy, fast response and long service life. BRIEF DESCRIPTION OF DRAWINGS

[0056] Figure 1 The luffing hydraulic system diagram of the preferred embodiment of the application;

[0057] Figure 2The control schematic diagram of the preferred embodiment of the present application;

[0058] Figure 3 The structure diagram of the variable amplitude of the tower crane jib;

[0059] Wherein: oil tank 1, motor 2, plunger variable pump 3, high pressure filter 4, first check valve 5, pressure gauge 6, pilot overflow valve 7, proportional directional valve 8, shuttle valve 9, second check valve 10, third check valve 11, oil return filter 12, variable amplitude cylinder valve group 13, variable amplitude cylinder 14, displacement sensor 15, first balance valve 13.1, first stop valve 13.2, second stop valve 13.3, second balance valve 13.4, safety valve 13.5, first pressure sensor 13.6, third stop valve 13.7, fourth check valve 13.8, fifth check valve 13.9, fourth stop valve 13.10, second pressure sensor 13.11. DETAILED DESCRIPTION

[0060] In order to make the technical means, creative features, purposes and effects of the present application easy to understand, the present application is further described below in combination with specific embodiments.

[0061] Embodiment 1, see Figure 1 and Figure 2 The variable amplitude hydraulic system of the tower crane jib shown in the drawings, comprising oil tank 1, motor 2, plunger variable pump 3, high pressure filter 4, first check valve 5, pressure gauge 6, pilot overflow valve 7, proportional directional valve 8, shuttle valve 9, second check valve 10, third check valve 11, oil return filter 12, variable amplitude cylinder valve group 13, variable amplitude cylinder 14 and displacement sensor 15;

[0062] Wherein: variable amplitude cylinder valve group 13 includes first balance valve 13.1, first stop valve 13.2, second stop valve 13.3, second balance valve 13.4, first pressure sensor 13.6, third stop valve 13.7, fourth check valve 13.8, fifth check valve 13.9, fourth stop valve 13.10 and second pressure sensor 13.11;

[0063] The hydraulic oil is stored in the oil tank 1, the motor 2 is connected with the plunger variable pump 3 through the shaft coupling, the oil suction port and the oil discharge port of the plunger variable pump 3 are connected with the oil tank 1 through the oil suction pipeline and the oil discharge pipeline respectively, the pressure oil port of the plunger variable pump 3 is connected with the inlet of the high-pressure filter 4, the outlet of the high-pressure filter 4 is connected with the inlet of the first one-way valve 5, the outlet of the first one-way valve 5 is divided into three paths, the first and second paths are connected with the pressure gauge 6 and the pressure port of the pilot overflow valve 7 respectively, the third path is connected with the P" port of the proportional directional valve 8, the 1 port of the shuttle valve 9 is connected with the B" port of the proportional directional valve 8 and is connected with the B1 port after confluence, the 2 port of the shuttle valve 9 is connected with the A" port of the proportional directional valve 8 and is connected with the A1 port after confluence, the middle 3 port of the shuttle valve 9 is connected with the pilot pressure oil port X of the plunger variable pump 3, preferably, the proportional directional valve 8 and the shuttle valve 9 are installed in a superimposed manner.

[0064] The oil discharge port of the pilot overflow valve 7, the T" port of the proportional directional valve 8, the inlet of the second one-way valve 10 and the outlet of the third one-way valve 11 are connected with the T3 port after confluence, the outlet of the second one-way valve 10 is connected with the oil tank 1 through the oil return filter 12, and the inlet of the third one-way valve 11 is connected with the oil tank 1 as the oil suction port; the A1 port and the B1 port are connected with the A2 port and the B2 port of the variable amplitude cylinder valve group 13 respectively, and the T2 port of the variable amplitude cylinder valve group 13 is connected with the T3 port.

[0065] The A2 port is connected with the 2 port of the first balance valve 13.1 and the 3 port of the second balance valve 13.4, and the 3 port of the second balance valve 13.4 is a pilot port; the B2 port is connected with the 2 port of the second balance valve 13.4 and the 3 port of the first balance valve 13.1, and the 3 port of the first balance valve 13.1 is a pilot port; the 1 port of the first balance valve 13.1 is divided into three paths and connected with the first stop valve 13.2, the check port of the fourth one-way valve 13.8 and the third stop valve 13.7 respectively; the 1 port of the second balance valve 13.4 is also divided into three paths and connected with the second stop valve 13.3, the check port of the fifth one-way valve 13.9 and the fourth stop valve 13.10 respectively; the other end of the third stop valve 13.7 is connected with the rodless cavity of the variable amplitude cylinder 14 and the first pressure sensor 13.6, and the other end of the fourth stop valve 13.10 is connected with the rod cavity of the variable amplitude cylinder 14 and the second pressure sensor 13.11; the other ends of the first stop valve 13.2 and the second stop valve 13.3 are connected in parallel, and then connected with the inlets of the fourth one-way valve 13.8 and the fifth one-way valve 13.9 after confluence and connected with the T2 port.

[0066] The application detects the oil pressure of the rodless cavity and the rod cavity of the amplitude cylinder 14 through the two ends of the shuttle valve 9, and when there is a difference between the pressures on both sides, the shuttle valve will automatically conduct the high-pressure side oil way and feed back the pressure signal to the pilot pressure oil port X of the plunger variable pump 3, so as to realize the dynamic adjustment of the pump displacement. The design ensures that the system can adjust the oil supply pressure in real time according to the load change through mechanical pressure comparison, improves the response accuracy of the amplitude action, and avoids the delay problem of the traditional electric control scheme.

[0067] In the embodiment, a safety valve 13.5 is further included, and the other end of the fourth stop valve 13.10 is connected to the rod cavity of the amplitude cylinder 14, the pressure port of the second pressure sensor 13.11 and the safety valve 13.5.

[0068] The other end of the first stop valve 13.2 and the second stop valve 13.3 is connected in parallel, and then connected to the inlet of the fourth one-way valve 13.8 and the fifth one-way valve 13.9, the unloading port of the safety valve 13.5 and the T2 port. The first stop valve 13.2 and the second stop valve 13.3 are used for unloading the pressure of the rodless cavity when the amplitude cylinder 14 is maintained. More specifically, when the amplitude cylinder 14 is maintained, the rodless cavity oil way is connected to the oil tank by manually opening the stop valve, so that the pressure in the cavity is quickly released, ensuring safe unloading. The safety valve 13.5 is used for quick overflow when the rod cavity of the amplitude cylinder 14 abnormally overpresses, eliminating the safety hazard of cylinder explosion caused by the instantaneous rise of the rod cavity pressure when the fourth stop valve 13.10 is mistakenly closed and the amplitude is operated to rise.

[0069] In the embodiment, the plunger variable pump 3 is a Rexroth A11VO-LRDS series axial plunger pump with a displacement of 40-260 ml / r and a maximum pressure of 350 bar, and has the functions of integrated power control, pressure cut-off and load sensing.

[0070] In the embodiment, the proportional directional valve 8 is a three-position four-way Y-type pilot proportional valve with an input of 4-20 mA current signal. When the current signal increases from 12 mA to 20 mA, the valve core is controlled to extend; when the current signal decreases from 12 mA to 4 mA, the valve core is controlled to retract.

[0071] In one embodiment, a PLC controller is further included, and the input end of the PLC controller is connected to the first pressure sensor 13.6, the second pressure sensor 13.11, the displacement sensor 15 and the amplitude up / down multi-gear switch signal set in the driver's room linkage platform.

[0072] The output end of the PLC controller is connected to the motor 2, the plunger variable pump 3 and the proportional directional valve 8. The PLC controller adjusts the displacement of the valve core of the proportional directional valve 8 through the current signal to realize the proportional control of direction and flow.

[0073] The first pressure sensor 13.6 is used for monitoring the pressure of the rodless cavity; the second pressure sensor 13.11 is used for monitoring the pressure of the rod cavity, and the displacement sensor 15 is used for monitoring the real-time stroke position of the variable amplitude oil cylinder 14.

[0074] As shown in Figure 3 one embodiment, the PLC controller is also used for calculating the variable amplitude angle according to the stroke signal received by the displacement sensor 15 and displaying it on the operation interface of the cab, and the calculation formula of the variable amplitude angle is as follows:

[0075] ,

[0076] wherein S is the oil cylinder length when the boom is horizontal; L1 is the support frame length;

[0077] L2 is the boom fulcrum length;

[0078] is the oil cylinder working stroke when the boom is variable amplitude;

[0079] α is the angle between the rod cavity fulcrum and the support frame when the boom is horizontal;

[0080] α' is the angle between the rod cavity fulcrum and the support frame when the boom is variable amplitude;

[0081] β is the angle between the rod cavity fulcrum and the boom when the boom is horizontal;

[0082] is the variable amplitude angle, which is the angle between the boom and the horizontal plane when the boom is variable amplitude.

[0083] By directly receiving the stroke signal of the displacement sensor 15 through the PLC controller, the variable amplitude angle of the swing arm is calculated in real time and displayed on the operation interface of the cab. Compared with the traditional measurement method which needs secondary conversion of the angle sensor, the accuracy is significantly improved. At the same time, the displacement data is multiplexed to the overspeed calculation function, which not only avoids the installation requirement of additional sensors, but also simplifies the system structure, realizes the efficient integration of single sensor dual-purpose.

[0084] In one embodiment, the PLC controller is also used to implement the over-grade shifting control of the variable amplitude hydraulic system: when over-grade upshifting, the PLC controller realizes the smooth transition of the current signal through the incremental ramp algorithm, so that the hydraulic oil flow output by the piston variable pump 3 is smoothly increased; when over-grade downshifting, the descending ramp algorithm is used, so that the hydraulic oil flow output by the piston variable pump 3 is smoothly decreased, for example: when switching from variable amplitude upshift 1 to variable amplitude upshift 3, the current signal output by the PLC controller to the proportional directional valve 8 is linearly increased from 14 mA to 18 mA within 2 s, ensuring that the hydraulic oil flow output by the piston variable pump 3 is smoothly increased during acceleration; similarly, when switching from variable amplitude upshift 3 to variable amplitude upshift 1 for deceleration, the current signal output by the PLC controller to the proportional directional valve 8 is set to descend linearly from 18 mA to 14 mA within 2 s, ensuring that the hydraulic oil flow output by the piston variable pump 3 is smoothly decreased during deceleration. The segmented ramp control strategy effectively suppresses the system impact caused by flow mutation during the variable amplitude process by dynamically adjusting the opening degree of the proportional valve, and ensures the stability of the actuator movement.

[0085] In one embodiment, the PLC controller is also used to implement pressure protection control: when the load pressure reaches the preset cut-off value of the piston variable pump 3, the safety valve of the piston variable pump 3 is opened to limit the system pressure; at the same time, the first pressure sensor 13.6 monitors the rodless cavity pressure in real time and transmits the signal to the PLC controller. If the rodless cavity pressure is abnormal or exceeds the threshold value, the PLC controller immediately triggers an alarm and executes a variable amplitude action stop instruction, forming a double safety guarantee mechanism of pressure cut-off and real-time monitoring, to ensure the safety and reliability of the system under overload conditions.

[0086] In one embodiment, the PLC controller is also used to implement intelligent stroke protection control: when the variable amplitude rises or falls, the stroke position approaches the preset protection threshold, the PLC controller immediately triggers a deceleration instruction to make the system run smoothly, for example, when the protection threshold is set to ±20 mm (the protection threshold can be adjusted according to different models), the first heavy protection of “about to overstroke” is triggered. At this time, the PLC controller will immediately intervene in the control and instruct the variable amplitude system to implement deceleration and smoothly stop running. By intervening in the process in advance, the mechanical impact and violent shaking of the variable amplitude system caused by the overstroke are effectively eliminated, ensuring the safety and stability of the equipment operation, avoiding the sudden stop impact caused by the direct cut-off of power by the traditional limit switch, and ensuring the safety and stability of the equipment operation.

[0087] In one embodiment, the PLC controller is also used to implement intelligent speed protection: in the case of unchanged gear, the PLC controller compares the gear normal speed with the real-time variable amplitude speed in real time: when the variable amplitude speed rises to 110% of the gear normal speed, the gear current increment received by the proportional directional valve 8 is reduced by 50%, the speed is automatically reduced, and the gear-up function is locked, and only gear-down speed reduction is allowed; when the variable amplitude speed recovers to the gear normal speed, the rated current is reset and the gear-up restriction is removed; if the variable amplitude speed continues to rise to 120% of the gear normal speed after the gear current increment is reduced by 50%, the PLC controller immediately stops the variable amplitude action and triggers an overspeed alarm. By setting the intelligent speed protection mechanism, when the variable amplitude speed exceeds 110% of the gear normal speed, the system automatically reduces the proportional directional valve current by half to achieve smooth speed reduction, and the gear-up function is locked to prevent misoperation; if the speed continues to rise to 120% of the gear normal speed, the action is immediately stopped and an alarm is triggered, forming a hierarchical protection. This strategy eliminates the response lag of the traditional system through real-time closed-loop regulation, uses gradient intervention to reduce mechanical impact, and has automatic recovery capability, which not only guarantees the operation safety, but also improves the operation continuity, and effectively reduces the overload risk.

[0088] The application also provides a control method applied to the tower crane boom luffing hydraulic system.

[0089] Boom up: the operator presses the "oil pump on" button, the PLC controller controls the motor 2 to be powered on, drives the plunger variable pump 3 to operate, the operator pulls down the boom up 1 gear on the linkage table, the PLC controller receives the switch quantity signal of the boom up 1 gear (the boom up gear control current signal is in the range of 12-20 mA, for example: if the boom up is set to 4 gears, the boom up 1 gear given current is 14 mA, the boom up 2 gear is 16 mA, the boom up 3 gear is 18 mA, and the boom up 4 gear is 20 mA), outputs the current signal corresponding to the gear to control the opening of the proportional directional valve 8, the plunger variable pump 3 outputs the hydraulic oil flow corresponding to the opening, and the hydraulic oil flow is sent to the rodless cavity of the boom cylinder 14 through the P" port, the A" port of the proportional directional valve 8, the first balance valve 13.1 and the third shut-off valve 13.7, and the second balance valve 13.4 is opened under the action of the pilot port pressure, the hydraulic oil in the rod cavity of the boom cylinder 14 flows back to the oil tank 1 through the fourth shut-off valve 13.10, the second balance valve 13.4, the B" port and the T" port of the proportional directional valve 8, the second one-way valve 10 and the oil filter 12, the boom cylinder 14 is pushed out, and the boom starts to rise;

[0090] In the boom luffing up process, the X port of the piston variable pump 3 receives the working oil pressure of the rodless cavity in real time through the shuttle valve 9, and based on the load sensing function, the pump body monitors the pressure difference between the input pressure and the output pressure of the proportional directional valve 8 in real time; when the pressure difference increases, the pump automatically reduces the displacement; when the pressure difference decreases, the displacement increases, and through dynamic adjustment, the pressure difference is always maintained at a set value. This closed-loop control keeps the pressure difference stable within the set range, avoiding overflow loss, ensuring the smoothness and control accuracy of the actuator movement, significantly reducing the heat generation of the luffing hydraulic system, prolonging the service life of the key components, and reducing the energy consumption of the whole machine;

[0091] During the boom luffing up period, the force direction and size of the luffing cylinder 14 are always changing. When the load of the luffing cylinder 14 is within the constant power control starting pressure range set by the piston variable pump 3, the piston variable pump 3 can output the maximum rated flow. At this time, the luffing speed is directly controlled by the luffing up gear of the linkage table. When the load exceeds the constant power starting pressure, the maximum output flow of the piston variable pump 3 will be automatically adjusted according to the power control characteristic curve. At this time, the constant power adjustment takes precedence over the gear adjustment, and the maximum luffing speed is dynamically limited to adapt to the increasing load, thereby ensuring the stability and reliability of the system operation;

[0092] During the boom luffing up period, according to the load and operation situation, if acceleration is required, the gear can be gradually switched;

[0093] During the boom luffing up process, when the load pressure reaches the preset pressure cut-off value of the piston variable pump 3, the safety valve of the piston variable pump 3 immediately opens to limit the pressure from rising, thereby ensuring the safety and reliability of the system under overload conditions. At the same time, the first pressure sensor 13.6 monitors the real-time pressure state of the rodless cavity in real time and transmits the pressure signal to the PLC controller. When the pressure of the rodless cavity is abnormal or exceeds the preset safety threshold, the PLC controller will trigger an alarm signal and execute a luffing action stop command according to the pre-set overpressure protection parameters, forming a double protection mechanism;

[0094] When the boom luffing up to the working position, the operator will turn the gear to zero position, the PLC controller outputs current signal according to the descending slope algorithm, controls the proportional directional valve 8 to smoothly switch to the middle position, and stops the boom luffing. At this time, the luffing cylinder 14 is locked and pressure maintained under the action of the first balance valve 13.1 and the second balance valve 13.4, and the motor delay power-off protection mechanism is triggered, ensuring the safety and stability of the system;

[0095] The control logic for boom lowering is symmetrical to that for boom raising.

[0096] In one embodiment, the control method further includes the following when the gear is skipped:

[0097] When the gear is shifted up, the PLC controller realizes the smooth transition of the current signal by the incremental ramp algorithm, so that the hydraulic oil flow output by the piston variable pump 3 is smoothly increased; when the gear is shifted down, the PLC controller realizes the smooth transition of the current signal by the decreasing ramp algorithm, so that the hydraulic oil flow output by the piston variable pump 3 is smoothly decreased.

[0098] In one embodiment, the control method further includes the following response when the amplitude approaches the limit stroke:

[0099] When the stroke position approaches the preset protection threshold during the amplitude rising or falling process, the PLC controller immediately triggers the deceleration instruction to make the system stop running smoothly.

[0100] In one embodiment, the control method further includes the following response when the amplitude cylinder 14 is in the air suction fault:

[0101] When the amplitude cylinder 14 is subjected to the same direction load during the boom amplitude rising, the oil tank 1 hydraulic oil is quickly sucked into the rodless cavity through the suction effect, the T5 port, the third one-way valve 11, the T3 port and the T2 port return pipeline, and the fourth one-way valve 13.7, so as to realize the oil supplement to prevent the amplitude instability; at the same time, under the condition that the gear is unchanged, the PLC controller compares the gear normal speed with the real-time amplitude speed in real time: when the amplitude speed rises to 110% of the gear normal speed, the gear current increment received by the gear proportional directional valve 8 is reduced by 50%, the speed is automatically reduced, and the gear-up function is locked, only the gear-down speed can be reduced; when the amplitude speed returns to the gear normal speed, the rated current is reset and the gear-up restriction is released.

[0102] If the amplitude speed continues to rise to 120% of the gear normal speed after the gear current increment is reduced by 50%, the PLC controller immediately stops the amplitude action and triggers the overspeed alarm;

[0103] When the air suction fault occurs during the boom amplitude falling, the rod cavity quickly supplements the oil through the fifth one-way valve 13.9, the PLC logic is symmetrical to the rising process, and the current adjustment and speed protection mechanism in the opposite direction are executed, forming a bidirectional and symmetrical fault protection system.

[0104] The above shows and describes the basic principles and main features of the present application and the advantages of the present application. It is obvious for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application includes the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any reference signs in the claims should not be regarded as limiting the claims involved.

[0105] Furthermore, it should be understood that although the specification is described in terms of embodiments, not every embodiment includes only one independent technical solution, and the specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that those skilled in the art can understand.

Claims

1. A hydraulic system for boom luffing of a tower crane, characterized in that: Includes an oil tank (1), a motor (2), a plunger variable pump (3), a high-pressure filter (4), a first check valve (5), a pressure gauge (6), a pilot-operated relief valve (7), a proportional directional valve (8), a shuttle valve (9), a second check valve (10), a third check valve (11), a return oil filter (12), a variable amplitude cylinder valve group (13), a variable amplitude cylinder (14), and a displacement sensor (15); Among them: the variable amplitude cylinder valve group (13) includes a first balance valve (13.1), a first shut-off valve (13.2), a second shut-off valve (13.3), a second balance valve (13.4), a first pressure sensor (13.6), a third shut-off valve (13.7), a fourth check valve (13.8), a fifth check valve (13.9), a fourth shut-off valve (13.10), and a second pressure sensor (13.11); Hydraulic oil is stored in the oil tank (1). The motor (2) is connected to the plunger variable pump (3). The oil suction port and oil discharge port of the plunger variable pump (3) are connected to the oil tank (1) through the oil suction pipe and the oil discharge pipe, respectively. The pressure oil port of the plunger variable pump (3) is connected to the inlet of the high pressure filter (4). The outlet of the high pressure filter (4) is connected to the inlet of the first check valve (5). The outlet of the first check valve (5) is divided into three paths. The first and second paths are connected to the pressure ports of the pressure gauge (6) and the pilot relief valve (7), respectively. The third path is connected to the P” port of the proportional directional valve (8). The 1 port of the shuttle valve (9) is connected to the B” port of the proportional directional valve (8), and after the flow is combined, it is connected to the B1 port. The 2 port of the shuttle valve (9) is connected to the A” port of the proportional directional valve (8), and after the flow is combined, it is connected to the A1 port. The 3 port of the shuttle valve (9) is connected to the pilot pressure oil port X of the plunger variable pump (3). The unloading port of the pilot-operated relief valve (7), the T” port of the proportional directional valve (8), the inlet of the second check valve (10), and the outlet of the third check valve (11) are connected to the T3 port after they converge. The outlet of the second check valve (10) is connected to the oil tank (1) via the return oil filter (12). The inlet of the third check valve (11) is used as the suction port to return to the oil tank (1). Ports A1 and B1 are connected to ports A2 and B2 of the luffing cylinder valve group (13) respectively. Ports T2 and T3 of the luffing cylinder valve group (13) are connected. Port A2 is connected to port 2 of the first balancing valve (13.1) and port 3 of the second balancing valve (13.4), with port 3 of the second balancing valve (13.4) serving as the pilot port; Port B2 is connected to port 2 of the second balancing valve (13.4) and port 3 of the first balancing valve (13.1), with port 3 of the first balancing valve (13.1) serving as the pilot port; Port 1 of the first balancing valve (13.1) is divided into three paths, connecting to the first shut-off valve (13.2), the check port of the fourth one-way valve (13.8), and the third shut-off valve (13.7), respectively; Port 1 of the second balancing valve (13.4) is also divided into three paths, connecting to... Connect the check port of the second shut-off valve (13.3), the fifth check valve (13.9), and the fourth shut-off valve (13.10); the other end of the third shut-off valve (13.7) is connected to the rodless chamber of the luffing cylinder (14) and the first pressure sensor (13.6); the other end of the fourth shut-off valve (13.10) is connected to the rod chamber of the luffing cylinder (14) and the second pressure sensor (13.11); the other ends of the first shut-off valve (13.2) and the second shut-off valve (13.3) are connected in parallel and then merged with the inlet of the fourth check valve (13.8) and the fifth check valve (13.9) before being connected to port T2.

2. The tower boom luffing hydraulic system according to claim 1, characterized in that: It also includes a safety valve (13.5), and the other end of the fourth shut-off valve (13.10) is connected to the rod chamber of the luffing cylinder (14), the second pressure sensor (13.11), and the pressure port of the safety valve (13.5); The other ends of the first shut-off valve (13.2) and the second shut-off valve (13.3) are connected in parallel and then merged with the inlet of the fourth check valve (13.8) and the fifth check valve (13.9) and the unloading port of the safety valve (13.5) before being connected to port T2.

3. The tower boom luffing hydraulic system according to claim 1, characterized in that: The variable displacement piston pump (3) is a Rexroth A11VO-LRDS series axial piston pump with a displacement of 40~260ml / r and a maximum pressure of 350bar. It integrates power control, pressure cut-off and load sensing functions.

4. The tower boom luffing hydraulic system according to claim 1, characterized in that: The proportional directional valve (8) is a three-position four-way Y-type pilot-operated proportional valve. It is input with a current signal of 4~20mA. The input is 12mA when the valve core is in the middle position. When the current signal increases from 12mA to 20mA, the control cylinder extends; when the current signal decreases from 12mA to 4mA, the control cylinder retracts.

5. The tower boom luffing hydraulic system according to claim 1, characterized in that: It also includes a PLC controller, whose input terminals are connected to the first pressure sensor (13.6), the second pressure sensor (13.11), the displacement sensor (15), and the variable amplitude rise / fall multi-position switch signal set on the driver's cab control panel. The output of the PLC controller is connected to the motor (2), the piston variable pump (3) and the proportional directional valve (8). The PLC controller adjusts the valve core displacement of the proportional directional valve (8) through the current signal to realize the proportional control of direction and flow. The first pressure sensor (13.6) is used to monitor the pressure in the rodless chamber; the second pressure sensor (13.11) is used to monitor the pressure in the rod chamber; and the displacement sensor (15) is used to monitor the real-time stroke position of the luffing cylinder (14).

6. The tower boom luffing hydraulic system according to claim 5, characterized in that: The PLC controller is also used to calculate the amplitude angle based on the stroke signal received by the displacement sensor (15) and display it on the operating interface in the driver's cab. The formula for calculating the amplitude angle is as follows: ， Where S is the length of the hydraulic cylinder when the boom is horizontal; L1 is the length of the support frame; L2 is the boom fulcrum length; This refers to the working stroke of the hydraulic cylinder during boom luffing. α is the angle between the fulcrum of the boom cavity and the support frame when the boom is horizontal; α' is the angle between the boom cavity fulcrum and the support frame when the boom is luffing; β is the angle between the boom and the fulcrum of the rod cavity when the boom is horizontal; The luffing angle is the angle between the boom and the horizontal plane when the boom is luffing.

7. A tower crane boom luffing hydraulic system according to claim 5, characterized in that: The PLC controller is also used to realize the cross-gear shifting control of the variable amplitude hydraulic system: when shifting up gears, the PLC controller realizes the smooth transition of the current signal through the incremental ramp algorithm, so that the hydraulic oil flow output by the piston variable pump (3) increases smoothly; when shifting down gears, the descending ramp algorithm is used to make the hydraulic oil flow output by the piston variable pump (3) decrease smoothly.

8. A tower crane boom luffing hydraulic system according to claim 5, characterized in that: The PLC controller is also used to implement pressure protection control: when the load pressure reaches the preset cut-off value of the plunger variable pump (3), the safety valve of the plunger variable pump (3) opens to limit the system pressure; at the same time, the first pressure sensor (13.6) monitors the rodless chamber pressure in real time and transmits the signal to the PLC controller. If the rodless chamber pressure is abnormal or exceeds the threshold, the PLC controller immediately triggers an alarm and executes the amplitude change action stop command, forming a dual safety protection mechanism of pressure cut-off and real-time monitoring to ensure the safety and reliability of the system under overload conditions.

9. A tower crane boom luffing hydraulic system according to claim 5, characterized in that: The PLC controller is also used to implement intelligent stroke protection control: when the stroke position approaches the preset protection threshold during the amplitude increase or decrease process, the PLC controller immediately triggers a deceleration command to make the system stop smoothly.

10. A tower crane boom luffing hydraulic system according to claim 5, characterized in that: The PLC controller is also used to realize intelligent speed protection: when the gear position remains unchanged, the PLC controller compares the normal speed of the gear position with the real-time variable speed in real time: when the variable speed rises to 110% of the normal speed of the gear position, the gear position current increment received by the proportional directional valve (8) of the gear position is reduced by 50%, the speed is automatically reduced, and the upshift function is locked, so that only downshifting and speed reduction are possible; when the variable speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is lifted. If the amplitude conversion speed continues to rise to 120% of the normal speed of the gear after the current increment of the gear decreases by 50%, the PLC controller will immediately stop the amplitude conversion action and trigger an overspeed alarm.

11. A control method applied to a tower crane boom luffing hydraulic system according to any one of claims 1-10, characterized in that: The control method includes: Boom raising: The operator presses the "oil pump on" button, the PLC controller controls the motor (2) to be energized, driving the piston variable pump (3) to run. The operator switches down the luffing rise gear 1 on the linkage table. The PLC controller receives the switch signal of luffing rise gear 1 and outputs the current signal corresponding to the gear to control the opening of the proportional directional valve (8). The piston variable pump (3) outputs the hydraulic oil flow corresponding to the opening, which passes through the P" port and A" port of the proportional directional valve (8) and the first balance valve (1). 3.1) The third shut-off valve (13.7) is connected to the rodless chamber of the luffing cylinder (14). At the same time, the second balance valve (13.4) is opened under the action of the pilot port pressure. The hydraulic oil in the rod chamber of the luffing cylinder (14) flows back to the oil tank (1) through the second check valve (10) and the return oil filter (12) from the B" port and T" port of the fourth shut-off valve (13.10), the second balance valve (13.4), and the proportional directional valve (8). The luffing cylinder (14) is pushed out, and the boom begins to rise. During the boom luffing process, the X port of the variable piston pump (3) receives the working oil pressure of the rodless chamber in real time through the shuttle valve (9). Based on its load sensing function, the pump body monitors the pressure difference between the input pressure and the output pressure of the proportional directional valve (8) in real time. When the pressure difference increases, the pump automatically reduces the displacement; when the pressure difference decreases, the displacement increases. Through dynamic adjustment, the pressure difference is always maintained at the set value. During the boom luffing and raising, the direction and magnitude of the force on the luffing cylinder (14) are constantly changing. When the load on the luffing cylinder (14) is within the constant power control starting pressure range set by the piston variable pump (3), the piston variable pump (3) can output the maximum rated full flow. At this time, the luffing speed is directly controlled by the luffing raising gear of the linkage table. When the load exceeds the constant power starting pressure, the maximum output flow of the piston variable pump (3) will be automatically adjusted according to the power control characteristic curve. At this time, constant power adjustment takes priority over gear adjustment. By dynamically limiting the maximum luffing speed, the load increases, thereby ensuring the stability and reliability of the system operation. During the boom luffing and raising process, the gears can be gradually switched if acceleration is required, depending on the load and operating conditions. During the boom luffing process, when the load pressure reaches the preset pressure cut-off value of the piston variable pump (3), the safety valve of the piston variable pump (3) immediately opens to limit the pressure from continuing to rise, thereby ensuring the safety and reliability of the system under overload conditions. At the same time, the first pressure sensor (13.6) monitors the real-time pressure status of the rodless chamber and transmits the pressure signal to the PLC controller. When the pressure in the rodless chamber is abnormal or exceeds the preset safety threshold, the PLC controller will quickly trigger an alarm signal and execute a luffing action stop command according to the preset overpressure protection parameters, forming a dual protection mechanism. When the boom rises to the working position, the operator switches the gear to the zero position. The PLC controller outputs a current signal according to the descending ramp algorithm, and controls the proportional directional valve (8) to smoothly switch to the neutral position, so that the boom luffing stops. At this time, the luffing cylinder (14) is locked and pressure-maintained under the action of the first balance valve (13.1) and the second balance valve (13.4), and at the same time triggers the motor delay power-off protection mechanism to ensure the safety and stability of the system. The control logic for boom descent is symmetrical with that for boom ascent. The PLC controller adjusts the opening of the proportional directional valve (8) in reverse through the current signal to control the retraction of the hydraulic cylinder.

12. The control method according to claim 11, characterized in that: The control method also includes handling situations where gears are shifted too quickly: When shifting up a gear, the PLC controller uses an incremental ramp algorithm to achieve a smooth transition of the current signal, so that the hydraulic oil flow rate output by the piston variable pump (3) increases smoothly; when shifting down a gear, a descending ramp algorithm is used to make the hydraulic oil flow rate output by the piston variable pump (3) decrease smoothly.

13. The control method according to claim 11, characterized in that: The control method also includes How to handle situations where the amplitude is close to its limit: When the amplitude increases or decreases and the travel position approaches the preset protection threshold, the PLC controller immediately triggers a deceleration command to bring the system to a smooth stop.

14. The control method according to claim 11, characterized in that: The control method also includes handling the air intake failure of the luffing cylinder (14): When the luffing cylinder (14) is subjected to the same load in the same direction and an extreme abnormal situation occurs during the luffing rise of the boom, it is quickly pulled out to suck air. The rodless chamber, through suction, quickly sucks the hydraulic oil from the oil tank (1) into the rodless chamber through the T5 port, the third check valve (11), the return oil pipes of the T3 port and the T2 port, and the fourth check valve (13.7) to replenish the oil and prevent the luffing from becoming unstable. At the same time, with the gear position unchanged, the PLC controller compares the normal speed of the gear position with the real-time luffing speed in real time: when the luffing speed rises to 110% of the normal speed of the gear position, the gear current increment received by the proportional directional valve (8) of the gear position is reduced by 50%, the speed is automatically reduced, and the upshift function is locked, so that it can only downshift and reduce speed. When the luffing speed returns to the normal speed of the gear position, the rated current is reset and the upshift restriction is released. If the amplitude conversion speed continues to rise to 120% of the normal speed of the gear after the current increment of the gear decreases by 50%, the PLC controller will immediately stop the amplitude conversion action and trigger an overspeed alarm. When a suction failure occurs during the boom luffing and descent, the rod chamber is quickly replenished with oil through the fifth check valve (13.9). The PLC control logic is symmetrical with the lifting process, and the current regulation and speed protection mechanisms are executed in opposite directions, forming a two-way symmetrical fault protection system.

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